Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $126.45   5.813%   $133.8005   $133.80   $133.80   $133.80  
  Purchase #2 $196.94   4.735%   $206.2651   $206.27   $206.25   $206.30  
  Purchase #3 $161.99   6.529%   $172.5663   $172.57   $172.55   $172.60  
  Purchase #4 $49.62   12.348%   $55.7471   $55.75   $55.75   $55.70  
  Purchase #5 $246.40   6.495%   $262.4037   $262.40   $262.40   $262.40  
  Purchase #6 $10.81   13.734%   $12.2946   $12.29   $12.30   $12.30  
  Purchase #7 $19.70   12.861%   $22.2336   $22.23   $22.25   $22.20  
  7 purchase totals = $811.91       $865.3109   $865.31   $865.30   $865.30